Although the majority of PEM fuel stacks are rectangular, cylindrical PEM fuel cell stacks are known. For example, passive, air-breathing cylindrical fuel cell stacks that are not humidified, cooled, or pressurized are described in U.S. Pat. Nos. 5,514,486 and 5,595,384. In these stacks annular fuel cell components are distributed along a common axis and held together by a single bolt extending between a pair of end-plates. A central, longitudinal fuel distribution manifold is connected to distribute fuel from a fuel inlet port (offset from the center of one of the end plates) axially along the stack and deliver fuel to fuel flow fields contacting the anodes. Air is supplied to the cathodes by passive diffusion from the stack periphery toward the center of the stack through porous flow fields. The fuel flow fields are sealed at the periphery of the stack, and the oxygen flow fields are sealed around the annular region or central opening, so both reactants are dead-ended. U.S. Pat. No. 6,773,843 describes a stack with similar architecture, but where the fuel is supplied from the center of the end-plate directly into the central, longitudinal fuel distribution manifold. Such passive, air-breathing stacks are generally capable of only relatively low power output. Also product water management and heat management can be challenging with this type of design.
Other cylindrical stacks include a solid oxide fuel cell (SOFC) or PEM fuel cell stacks that have a central internal manifold that is split into two compartments for supplying both fuel and oxidant to a plurality of annular anode and cathode plates, respectively, such as described in U.S. Pat. Nos. 5,549,983 and 6,291,089. In this stack design both fuel and oxidant flow radially from the center to the periphery of each fuel cell in a co-flow configuration. This design is not dead-ended on either reactant (although the intention is that the fuel is almost completely consumed), and the spent reactant streams exit the periphery of the stack into an enclosing vessel, where they are combined and discharged via a single exhaust port. In some embodiments the enclosing vessel houses more than one stack, and the interior of the vessel is subdivided to form separate fuel supply, oxidant supply and reactant exhaust compartments, each with an associated external port.
The routing and distribution of the reactant streams is a significant challenge with existing cylindrical fuel cell stack architectures. The challenges include ensuring sufficiently uniform flow distribution within and among individual fuel cells in the stack, and providing effective sealing to prevent mixing of the fuel and oxidant streams.
The present invention relates to a cylindrical, hexagonal and other fuel cell stack architectures with improved routing and distribution of the reactant streams. These fuel cell stack architectures offer other advantages as described herein. One or more stacks can be incorporated into a self-contained fuel cell power module which is convenient to use, and is scalable for different end-use applications.